Present mobile product application control systems are generally designed for simple closed loop control of a multiple loop network or are otherwise directed generally toward a single open loop distributed network. At present, the maximum amount of loops that can be added to a multiple closed loop network typically would approach ten. Beyond this value, the overall packet structure and network control would become cumbersome, requiring significant redesign of the overall closed loop system.
A typical closed loop system is laid out with a host controller located within the cab of a vehicle, made up of a processor with associated input and output devices. This host controller is typically directly linked to a second controller located within the cab, which is responsible for all communication to devices on the chassis of the vehicle. Such a system is shown in U.S. Pat. No. 4,630,773 to Ortlip, issued Dec. 23, 1986 entitled "Method and Apparatus for Spreading Fertilizer." Another system is shown in U.S. Pat. No. 5,220,876 to Monson et al., issued Jun. 23, 1993 entitled "Variable Rate Application System" and assigned to the Assignee of the present invention. Both the '773 and '876 patents are incorporated herein by reference in their entirety.
In closed loop systems such as those stated above, the addition of loops as a result of further control requirements adds great complexity to the system wiring. This results in a realistic limit to the amount of loops that can be added to a single system. Beyond this limit, the amount of wiring becomes too great and routing the wiring is a considerable challenge. At present, it is felt that ten loops is the approximate limit for a single host system for the type described above.
Software construction also places many constraints on the design and application of a control system. The common top down design has certain flow characteristics that define a specific flow path within the operating system. This also limits the effective amount of devices that can be controlled with a single system, as eventually the communication link to the devices becomes the limiting factor.
The aforementioned software construction implies that any changes in the requirements, such as the inclusion of an additional loop on the vehicle, often causes sweeping changes within the code. This also has obvious trickle-down effects that are not desired within the flow structure of the program.
Thus, debugging and testing become required parts of the system maintenance, requiring large amounts of capital and time to assure a simple change has not caused greater errors elsewhere in the system (often occurring in totally unrelated places).
One solution to the many problems stated herein before was addressed in U.S. Pat. No. 5,630,924, to Monson et al., issued Sep. 26, 1995, entitled "Mobile Control System Responsive to Land Area Maps", and assigned to the Assignee of the present invention. The '924 patent is incorporated by reference in its entirety herein. The inventive system disclosed and claimed by Monson et al. in the '924 patent effectively eliminated the requirement for multiple closed loops by utilizing a single open loop distributed network. This was accomplished with the use of modern hardware and software capabilities. In particular, the system utilized object oriented software design as well as Microsoft.RTM. Windows.RTM. interfacing, distributed network controls and Echelon.TM. LonWorks.TM. network technology.
For the aforementioned reasons, it becomes immediately apparent that existing closed loop product application control system designs are by no means desirable, and entirely new approaches are required. While the solution provided by Monson et al. in the '924 patent addressed many of the problems associated with closed loop product application control systems, a need still exists for a system architecture which, to a great extent, is independent of the media and network protocol utilized. The present invention described in detail hereinafter offers an additional solution to the stated problems.